Blow-off system for multi-stage turbo compressor

ABSTRACT

The present invention relates to a blow-off system for a multi-stage turbo compressor that includes a plurality of blow-off pipes disposed according to respective stages of the multi-stage turbo compressor; a plurality of blow-off valves disposed correspondingly to the plurality of blow-off pipes; and a plurality of nozzles disposed at the front or back sides of the plurality of blow-off valves and adapted to prevent the generation of surge.

TECHNICAL FIELD

The present invention relates to a blow-off system for a multi-stageturbo compressor that is mounted to perform rapid transformation to loadand no load and to reduce the load of a bearing upon the transformation,the blow-off system including: a plurality of blow-off pipes disposedaccording to respective stages of the multi-stage turbo compressor; aplurality of blow-off valves disposed correspondingly to the pluralityof blow-off pipes; and a plurality of nozzles disposed at the front orback sides of the plurality of blow-off valves, thereby preventing thegeneration of surge.

BACKGROUND ART

Unlike a reciprocating compressor or a screw compressor, a multi-stageturbo compressor has a minimum flow rate value at a specific pressurebecause surge is generated.

During the operation of the compressor, if the flow rate is decreasedand the surge is sensed, air blows off toward atmosphere or an inlet,thereby escaping from the surge, such that a revolution is reduced tostand by at a no load state.

Conventionally, as shown in FIG. 1, a blow-off valve 3 is disposed on abranch pipe, and the opening and closing speed of the blow-off valve 3is appropriately set, thereby applying no impact to the compressor andpreventing the occurrence of the surge.

According to the conventional system as shown in FIG. 1, a relativelylarge valve is capable of blowing off at a sufficiently high flow rateso as to avoid one-stage surge at a low pressure like a low speed surgearea as shown in FIG. 3, thereby being lowering to an area where thepressure is low and the flow rate is high. However, when the blow-offvalve is closed to change to load, the pressure is momentarily increasedto apply much load to a bearing, and especially, if an impeller isdisposed at the both sides of a shaft, thrust load is drasticallyincreased at a position of a convection quantity at a low pressure.

If a relatively small valve is employed to decrease the blow-offquantity, the impact applied during the valve is opened and closed issmall, but while the revolution is being increased, a low speed surgearea is suffered at a low revolution. Thus, so as to avoid the surge,the revolution should be reduced up to no load at the expense of asubstantially long period of time.

More specifically, if a bearing having a relatively large supportingforce like an air foil bearing is employed, a momentary pressurevariation causes the bearing to be burnt or damaged, such that asubstantially large thrust bearing supporting force is needed.

According to the prior art disclosed in Japanese Patent Publication No.10-089296 (dated on Apr. 7, 1998), a blow-off valve and an adjustingplate are disposed on an outlet pipe, but they are not adapted toprevent surge, but adapted to control an amount of air discharged bymounting a nozzle in the middle portion thereof, thereby functioning asa cooling air extracting system for cooling a motor or a magneticbearing.

According to another prior art disclosed in International PatentApplication No. PCT/KR2007/005663 (filed on Nov. 12, 2007), further, aflow rate-controlling nozzle is disposed at the front or rear side of ablow-off valve, thereby rapidly responding to the generation of thesurge. However, the prior art blow-off system is applicable to asingle-stage compressor, and it has the limited operating range by theone-stage surge in a multi-stage compressor. Therefore, so as to avoidthe limitation of the operating range, the nozzle should be disposed ateach of the multiple stages of the multi-stage compressor, therebyrapidly responding to the generation of the surge.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention has been made in view of theabove-mentioned problems occurring in the prior art, and it is an objectof the present invention to provide a blow-off system for a multi-stageturbo compressor that is mounted to perform rapid transformation to loadand no load and to reduce the load of a bearing upon the transformation,the blow-off system including: a plurality of blow-off pipes disposedaccording to respective stages of the multi-stage turbo compressor; aplurality of blow-off valves disposed correspondingly to the pluralityof blow-off pipes; and a plurality of nozzles disposed at the front orback sides of the plurality of blow-off valves, thereby preventing thegeneration of surge.

Technical Solution

To achieve the above object, according to the present invention, thereis provided a blow-off system for a multi-stage turbo compressor thatincludes a plurality of blow-off pipes disposed according to respectivestages of the multi-stage turbo compressor; a plurality of blow-offvalves disposed correspondingly to the plurality of blow-off pipes; anda plurality of nozzles disposed at the front or back sides of theplurality of blow-off valves.

Advantageous Effects

According to the present invention, a first blow-off valve and a firstnozzle are adapted to stop the blowing near a maximum availablepressure, thereby reducing the impact, and a second blow-off valve and asecond nozzle are adapted to conduct the blowing while avoiding thesurge of a first stage of the compressor at a low speed area, therebyrapidly lowering a revolution to no load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a conventional blow-off system.

FIG. 2 is a schematic view showing a blow-off system for a multi-stageturbo compressor according to the present invention.

FIG. 3 is a graph showing the performance curves of the blow-off systemfor a multi-stage turbo compressor according to the present invention.

MODE FOR THE INVENTION

Hereinafter, an explanation on a blow-off system for a multi-stage turbocompressor according to the present invention will be given withreference to the attached drawings.

As shown in FIG. 2, there is provided the blow-off system has an on/offtype first blow-off valve 4 and a first nozzle 14 at the front or rearside of the first blow-off valve 4 and an on/off type second blow-offvalve 5 and a second nozzle 15 disposed at the front or rear side of thesecond blow-off valve 5, so as to control the flow rate passedtherethrough by two stages.

A first problem where the surge on a first stage of the compressor at alow revolution is generated is solved by opening all of the first andsecond blow-off valves 4 and 5 and the first and second nozzles 14 and15, thereby enlarging a sufficient blowing area, a second problem wherethe impact is generated during loading is solved by closing the secondblow-off valve 5 and the second nozzle 15 and next by closing the firstblow-off valve 4 and the first nozzle 14 after acceleration, therebydistributing the impact, and a third problem where the surge isgenerated during unloading is solved by opening all of the first andsecond blow-off valves 4 and 5 and the first and second nozzles 14 and15 at a time and at the same time by conducting the deceleration,thereby enlarging a sufficient blowing area and simultaneously rapidlyachieving the deceleration, without any exceeding to a thrust protectionline.

An activating algorism of the compressor is in detail illustrated by theperformance curves as shown in FIG. 3, and the processes are as follows:

A) Loading Process

(1) If power is applied, all of the first and second blow-off valves 4and 5 and the first and second nozzles 14 and 15 are opened.

(2) If an activating signal is applied, the revolution is accelerated toP1 and stand-by is conducted to a no load state.

(3) If a loading signal is applied, the revolution is accelerated to P2.

(4) The second blow-off valve 5 and the second nozzle 15 are closed andthe revolution is accelerated to P3.

(5) The revolution is accelerated to P4.

(6) The first blow-off valve 4 and the first nozzle 14 are closed tostop the blowing and to provide compressed gas.

B) Unloading Process

(1) The revolution is conducted at P6 and if an unloading signal isapplied, all of the first and second blow-off valves 4 and 5 and thefirst and second nozzles 14 and 15 are opened and at the same time therevolution is reduced, thereby avoiding the thrust protection line andmoving the revolution to P7.

(2) The revolution is rapidly decreased to P2.

In the above-mentioned description, the two-stage compressor, which hasthe first and second blow-off valves 4 and 5 and the first and secondnozzles 14 and 15, is employed as the multi-stage compressor, but it ispossible that the number of the valves and nozzles is freely adjustedaccording to the number of stages of the compressor.

1. A blow-off system for a multi-stage turbo compressor comprising: aplurality of blow-off pipes disposed according to respective stages ofthe multi-stage turbo compressor; a plurality of blow-off valves (4 and5) disposed correspondingly to the plurality of blow-off pipes; and aplurality of nozzles (14 and 15) disposed at the front or back sides ofthe plurality of blow-off valves (4 and 5) so as to prevent thegeneration of surge.